This invention relates to apparatus for the cutting through of a pile of sheets with a disk-knife or revolving blade, the circumference of which forms a smooth circular cutting edge and to a conveying apparatus which feeds the pile of sheets to the revolving blade and clamps the pile of sheets between the confronting surfaces of two conveyor elements.
In the description which follows, the term "pile of sheets" shall mean any pile or set of sheets or folios which lie on top of each other, for example, a book, a sheet folded several times, a brochure, a booklet, a signature and the like. A "brochure" or "booklet", as used herein, is defined as a pile of sheets consisting of sheets placed on top of each other all of which are folded around a common fold forming the back of the brochure or booklet. The folios or sheets forming the brochure or booklet can be stapled or glued together at the back, however, they may also be joined loosely together. Such a brochure or booklet may be called a "signature". The term "cutting through a pile of sheets" shall, as used herein, also include the so-called "trimming" in which the edges of a pile of sheets, for example, the edges of a brochure are trimmed since, even when only its edges are trimmed, the entire pile of sheets must be cut through.
In the prior art, it is known, for example, to trim brochures at their edges or to cut them in the middle with the use of disk-knives arranged at the delivery end of folding machines. In the case of the known devices, a cylindrical counter-knife is associated with each disk-knife. The disk-knife for cutting through of the booklet has a circumferential cutting edge having a cross-section forming an acute angle and the side of which facing the counter-knife is planar. The counter-knife is formed by a circumferential edge, substantially right-angled in cross-section, of a cylinder which, together with a second cylinder concentric to the axis of the disk-knife, forms a clamping-slit for the brochure. Within increasing thickness of the brochure, the point at which the disk-knife begins its cut is shifted farther and farther away from the clamping-slit in a direction opposite to that in which the booklet advances so that the disk-knife must penetrate into the brochure at a point where it is neither supported by the counter-knife nor clamped in the clamping-slit. The consequence is that at the point of penetration of the disk-knife, the individual sheets of the brochure are not secured against displacement relative to each other. Thus, as the disk-knife penetrates into the booklet, the position of the sheets is distorted and the cut necessarily becomes more and more irregular with increasing thickness of the brochure.
In the case of folding machines, a somewhat irregular cut has little significance because the brochures or booklets are usually units or sections of books which, after having been bound, are again trimmed by means of a guillotine knife.
A device of the aforementioned type is described, for example, in Swiss Pat. No. 383,331 wherein there is disclosed that, with these known devices, when greater feeding speeds are applied, i.e., a higher cutting power is achieved, excessive heat develops at the cutting edge so that if the blade edge is not made of hard metal, it will anneal and lose its hardness. The use of hard metal blades is, however, not feasible because of the high manufacturing costs for such blades. In Swiss Pat. No. 389,574, there is disclosed a cutting device for blocks of books and mentioned therein is a revolving blade of the type used in meat slicing machines for the cutting of, for example, cold cuts and ham. This patentee states that such a revolving blade cannot be used as a cutting knife for blocks of books because the blade, when cutting through paper, wears out rapidly and must be frequently reground.
In view of the aforesaid reasons set forth in these prior art patents, heretofore, only disk-type milling cutters have been used for the cutting of the backs of books. Such cutters are actually most suitable for the cutting of backs of books where a rough-cutting surface is desired for the subsequent gluing together of the individual sheets of the book. These known cutting devices are not, however, suitable for cutting of the upper and lower edges of a booklet and the edge opposite the back of a booklet because a smooth cut surface is desired on these edges since they remain visible.